The present invention relates generally to electronically controlled engine compression release brakes, and more particularly to an electronic control strategy for transitioning between single event and dual event engine braking.
Single event engine compression release braking refers to the practice of operating an engine as an air compressor in a way that induces a retarding torque on the engine. This retarding torque translates into work machine braking when the engine is coupled to the machine""s wheels or tracks by being in gear in a conventional manner. In typical single event engine braking, the exhaust valve is held closed during a portion of the engine""s compression stroke. Sometime before the piston reaches top dead center, the exhaust valve is opened, and the compressed air in the cylinder is blown down into the exhaust line. The braking horsepower achieved by such an event is sensitive to several variables such as ambient pressure, ambient temperature, engine speed, etc., but is likely most sensitive to the timing of when the blow down event occurs. For instance, When blow down occurs near top dead center, the maximum braking horsepower is achieved; however, when the timing of the blow down event is advanced, the braking horsepower is correspondingly reduced since the pressure at blow down decreases with advances in blow down timing.
In recent years, engineers have discovered a way to increase engine braking horsepower by increasing the mass of air and initial pressure of the same toward the beginning of a compression stroke. This so called dual event engine braking briefly opens the exhaust valve near bottom dead center near the beginning of the compression stroke. This boosting portion of the dual event engine braking is timed to coincide with the blow down event of another cylinder such that the pressure wave from the blow down cylinder raises the initial pressure in the first cylinder. The blow down portion of the dual event engine braking is performed much in the same manner as a single event exhaust braking. In other words, if blow down occurs near top dead center, a maximum braking horsepower is achieved. As timing of the blow down event advances, braking horsepower correspondingly decreases. Because of the added mass to the cylinder and the increased initial pressure, dual event engine braking can produce braking horsepower as much as 15% or more over single event engine braking. A more detailed discussion of dual event engine braking is contained in co-owned U.S. Pat. No. 5,724,939 to Faletti et al.
While dual event engine braking can substantially increase engine braking horsepower, it can cause problems with other engine related components. For instance, fuel injector tips that are positioned in the engine cylinders but not brought into play during engine braking can experience substantial temperature increases as a result of engine braking, and especially as a result of dual event engine braking. The reasons for the substantial increase in injector tip temperatures are twofold. First, when the injector is operating when the engine is in a power mode, each injection spray carries some heat away from the injector tip, and serves as a threshold means of injector tip cooling. During engine braking, no injection takes place and thus this secondary cooling phenomenon attributed to fuel injection does not occur. When this factor is combined with the fact that air in the cylinder during dual event engine braking is substantially hotter than single event engine braking, the injector tip can run the danger of exceeding its tempering temperature, especially during sustained dual event engine braking at higher engine speeds.
If the injector tip exceeds its tempering temperature, it can lose its hardness at critically stressed areas, such as the needle valve seat. If this occurs, potentially catastrophic damage can occur due to potential tip failures from accelerated fatigue in the region of the needle valve seat. Other potential obstacles to the successful incorporation of dual event engine braking into practical use include excessive noise and possible turbine overspeed.
The present invention is directed to overcoming one or more of the problems set forth above.
In one aspect of the invention, a method of engine braking includes an initial step of determining whether fuel injector tip temperatures are at or above a predetermined temperature. If the injector tip temperatures are at or above the predetermined temperature, then single event engine braking is performed. If the injector tip temperatures are below the pre-determined temperature, then dual event engine braking is performed.
In still another aspect, a work machine includes an engine attached to a work machine housing. A plurality of electronically controlled engine brake actuators are attached to the engine. A plurality of fuel injectors are also attached to the engine. An electronic control module is in control communication with the plurality of electronically controlled engine brake actuators. The electronic control module includes means for transitioning from dual event engine braking to single event engine braking when tips of the fuel injectors are at or above a pre-determined temperature.
In another aspect of the invention, an electronic control module includes a means for determining whether fuel injector tip temperatures are at or above a predetermined temperature. In addition, the electronic control module includes means for commanding single event engine braking if the injector tip temperatures are at or above the pre-determined temperature. Also included is a means for commanding dual event engine braking if the injector tip temperatures are below the pre-determined temperatures.